The present invention relates to an aortic stent-graft calibration model for the calibration of different imaging modalities and to a stent-graft training model for enabling pre-operative surgical practice for successful stent deployment for repair of an abdominal aortic aneurysm (AAA).
The need for repair of an abdominal aortic aneurysm (AAA) in patients has been recognized for many years in the medical field. Abdominal aortic aneurysms (AAA) affect a significant portion of the elderly population. Surgical repair of an abdominal aortic aneurysm (AAA) has a much higher mortality rate than less invasive techniques, such as deployment of a stent through a femoral artery.
Essential to the successful placement of a stent for repair of an abdominal aortic aneurysm (AAA) are pre-operative imaging modalities. The four most utilized imaging modalities in the medical field are contrast aortography (CA), spiral computed tomography (CT), magnetic resonance imaging (MRI), and intravascular ultrasonography (IVUS).
These four imaging modalities assess the diameter of the aneurysmal portions of the aortic system, the diameter and length of the nonaneurysmal proximal neck for anchoring the stent, the diameter and length of the distal aortic/iliac neck, and the total length of the prosthesis required for spanning the length of the aneurysm with fixation into normal arterial tissue proximally and distally of the aneurysm. Any inaccuracy in the equipment of the imaging modalities may adversely affect the successful repair of the abdominal aortic aneurysm (AAA) in a patient and increase the risk for major abdominal surgery with its associated mortality rate.
Due to the use of the four imaging modalities in the repair of an abdominal aortic aneurysm (AAA) in a patient, there is a need for accurately calibrating the equipment of all four imaging modalities to insure successful deployment of the stent. Additionally, it is highly desirable for training purposes to simulate the introduction of a guidewire and catheter for deployment of the stent for repair of an abdominal aortic aneurysm (AAA) on a model before performing the procedure on a patient. The present invention provides a calibration model that can be utilized to calibrate the equipment of all four imaging modalities as well as a training model to simulate stent deployment before the procedure is performed on a patient.
In accordance with the present invention, an aortic stent-graft calibration model is provided for the calibration of the equipment of four widely utilized testing modalities. In addition, an aortic stent-graft training model is provided for effective simulation of deployment of a stent for repair of an abdominal aortic aneurysm (AAA).
In general, the aortic stent-graft calibration model provides an aortic model with aneurysms constructed of a suitable material to permit imaging of the model from a desired imaging modality such as CA, CT, MRI or IVUS. In order to permit calibration of the imaging apparatus used in the selected modalities, the calibration model includes reference indicia at selected locations to provide fixed spatial measurements on the model. The reference indicia are selected so that the indicia are discernable in the image of the model. After the model has been imaged, the actual spatial measurements from the model can be compared to corresponding spatial measurements of the images of the reference indicia taken from the image of the model to detect any difference between the actural locations of the reference indicia on the model and the image locations of the indicia from the model image. In a specific embodiment of the present invention, the aortic stent-graft calibration model comprises a hollow, tubular Y-shaped core having interior and exterior surfaces conforming to the desired shape of a predetermined aorta with selectively positioned and sized aneurysms. The core is comprised of silicone to permit accurate imaging by at least one imaging modality and desirably multiple imaging modalities. An external frame holds the core in a fixed position. The frame is made from a simulated material that does not smash or obliterate the core during imaging or at least is distinguishable from the core in a selected imaging modality. For this purpose, the tubular core of the aortic stent-graft calibration model is mounted in a clear block of suitable material for imaging by the desired imaging modality. For example, the block may be in the form of an acrylic container filled with silicone gel for encasing and suspending the silicone core. To enable the model to be used in calibration of imaging modalities, marking indicia in the form of marking rings are provided at selected locations on the model as reference points for dimensional measurements for comparison to corresponding points on images obtained by the selected imaging modality.
The aortic stent-graft calibration model is produced in a series of steps. First, a rigid skeleton or Y-frame is assembled from hollow plastic piping encased in rubber tubing. The Y-frame is repeatedly dipped in melted wax to achieve a uniform thickness over the contour of the Y-frame. Holes are then made through selected locations of the Y-frame to mark the sites for reference indicia used to acquire dimension measurements and to obtain actual length measurements.
A one-piece silicone mold is formed about the wax covered Y-frame. The Y-frame is then removed from the one-piece silicone mold and a solid polyurethane core is cast from the mold. Wall thickness and aneurysmal segments are then applied to the outer contour of the polyurethane core with melted wax. A two-piece mold of polyurethane is formed about the polyurethane core and the applied wall thickness and aneurysmal segments of wax. The polyurethane core, together with the applied wall thickness and aneurysmal segments of wax, is removed from the two-piece polyurethane mold. The applied wall thickness and aneurysmal segments of wax are removed from the polyurethane core and the wax-coated polyurethane core is placed back in the two-piece polyurethane mold. The space where the wall thickness and aneurysmal segments of wax previously existed is filled with silicone. The polyurethane core with the applied wall thickness and aneurysmal segments of silicone is removed from the mold. The polyurethane core is then removed leaving a hollow tubular Y-shaped core of silicone wall thickness and aneurysmal segments.
The aortic stent-graft calibration model can be utilized to calibrate the equipment of various imaging modalities such as contrast aortography (CA), spiral computed tomography (CT), magnetic resonance imaging (MRI), and intravascular ultrasonography (IVUS). First, reference indicia are applied to the model at the locations corresponding, or at least correlating, to the marked sites made on the initial skeleton. For example, marking rings are attached to selected locations on the model in positions related to the locations of the marked sites on the skeleton. The marking indicia are then filled with contrast agents to permit accurate imaging by the different testing modalities.
The four imaging modalities are then performed on the model. Selected measurements obtained from the acquired images of the referenced indicia of the model from the imaging modalities are compared to the actual dimensions from the model. The equipment of each imaging modality can then be calibrated accordingly.
A model in accordance with the present invention can also be utilized as an aortic stent-graft training model to simulate introduction and placement of a guidewire and catheter for deployment of a stent for repair of an abdominal aortic aneurysm (AAA). In general, the training model comprises two mating halves defining an inner lumen having a contoured inner wall surface in the shape of an aorta with selectively positioned aneurysms. During simulation, a stent can be deployed in the lumen of the model through use of the guidewire and catheter. The model can then be separated into two pieces so that the exact location of the stent may be checked by direct inspection of the model. By opening the model, the stent may also be retrieved for additional practice.
In a specific embodiment of the invention, the aortic stent-graft training model includes two mating halves each providing one half of a hollow, tubular Y-shaped core configured in the shape of a predetermined aorta with selectively positioned and sized aneurysmal segments. An external framing structure is provided for the core. For this purpose, the core of the aortic stent-graft training model is mounted in two mating blocks. The model halves are openable to permit stent retrieval after a practice deployment of the stent in the core of the model. The two mating halves of the model may be formed from a suitable material so that the blocks may be held together by suction. When the two halves are pressed together, the hollow core is accessible from the exterior of the model to permit access to the lumen of the core for deployment of a stent. The hollow core of each mating half has an arterial wall thickness and aneurysmal segments. The inner contour of each core registers with the inner contour of the other core to provide proper alignment of the aorta and the aneurysmal segments. For this purpose, the core of the model is hollow; the blocks are in the form of translucent acrylic containers filled with polyurethane.